X-ray CT (Computed Tomography) devices include an X-ray source that irradiates an object with X-rays, and an X-ray detector for imaging an object which is disposed at a position opposite to the X-ray source and for detecting X-rays passing through the object. Such devices reconstruct the differences in the X-ray absorption ratio inside the object as images using a data processing system based on projected data in plural directions obtained by rotational imaging around the object.
In general, the X-ray source uses an X-ray tube that emits electrons accelerated by a high voltage to a positive electrode in order to generate X-rays. However, with respect to the energy used for accelerating the electrons, the generating efficiency of X-rays is low, and most energy is converted into heat. Hence, a phenomenon occurs which shifts the source where X-ray beams are generated due to the thermal expansion of the heated positive electrode.
In order to eliminate the negative effect of such a positional shift of an X-ray focal point and to reduce false images (or artifacts) generated in a reconstructed image, it is necessary to detect the positional shift of the X-ray focal point, and to control the position of the X-ray focal point or to correct measured data.
A detector (hereinafter, referred to as a shift detector) for detecting the positional shift of the X-ray focal point employs a configuration in which equal to or greater than two X-ray detector elements are disposed side by side, and measures the irradiation center of X-rays, i.e., the focal point based on a difference between output signals by respective X-ray detector elements.
Moreover, positional control of the X-ray focal point includes, for example, a method of moving the X-ray tube to the irradiation center or a method of moving a collimator that restricts the X-ray beam range.
Regarding conventional measurement and correction of the positional shift of the X-ray focal point using a shift detector, for example, Patent Literature 1 and Patent Literature 2 disclose X-ray CT devices, respectively. Moreover, regarding a technology of correcting scattered X-rays generated from an object, etc, for example, Patent Literature 3 and Patent Literature 4 disclose a CT scanner and an X-ray CT device, respectively.